There has long been the requirement for laminating separate, continuous webs together while controlling the longitudinal alignment or registration between the webs so that they are joined at a desired point. Most often this occurs in systems requiring the repetition or repeating of a structure or printed pattern on one web, with corresponding structure or pattern on the second web. The length of the respective patterns is called the repeat length. The repeat length of one web is often held constant and used as the reference for the other web. This is called the "design repeat length". The printed pattern on the second web to be adjusted to the design repeat length is called the "actual repeat length" of that web. Proper registration between two joined webs require that the actual repeat length be maintained equal to the design repeat length.
The use of a pre-printed material in a continuous web form is desired for its economy; however, because the web is of one continuous length and is not cut until after it is laminated, there is a problem with adjusting the actual repeat length to the design repeat length without stopping the process. This problem is most commonly overcome by making at least one web of a stretchable material and printing the repeat length on that web much shorter than the design repeat length. Tension is then applied to the stretchable material while it is running to make the under-dimensioned repeat length on that web greater, until it matches the actual design length required by the second web. It is known, therefore, to regulate the tension of a stretchable web to vary the design repeat length. In this way, adjustments can be made for inconsistencies in the production of the web and other manufacturing variables that require registration correction.
A problem exists, however, because some types of web materials, such as aluminum foil, are only marginally stretchable. This permits a very limited range of adjustment by web stretching. There has long been sought a way to change the actual repeat length of a pre-formed, continuous web while in motion with respect to a pre-formed second web when neither of the webs is easily stretchable.
Prior art patents which are considered relevant to but not anticipatory of the applicant's invention include: U.S. Pat. No. 3,762,125 to Prenna, entitled "Film Registration Apparatus"; U.S. Pat. No. 3,294,301 to Richter, entitled "Web Registration System"; U.S. Pat. No. 3,589,095 to James, entitled "Method and Apparatus for Registering Two Separate Webs of Wrapping Material"; and U.S. Pat. No. 4,704,171 to Thompson et al, entitled "Laminating Device with Paper Tension Control".